Gravity casting refers to the process of injecting molten metal into the mold under the action of the earth's gravity, also known as gravity casting. Generalized gravity casting includes sand mold casting, metal mold casting, investment casting, lost foam casting, mud mold casting, etc; Narrow sense of gravity casting mainly refers to metal mold casting. The mold of metal mold can be used repeatedly. Each time the molten metal is poured, a casting can be obtained. The service life is very long and the production efficiency is very high. The castings of metal mold not only have good dimensional accuracy and smooth surface, but also have higher strength than those of sand mold when pouring the same liquid metal. Therefore, in mass production of medium and small castings of non-ferrous metals, as long as the melting point of the casting material is not too high, metal mold casting is generally preferred